This invention relates to optical surfaces commonly referred to as Fresnel surfaces. Fresnel surfaces are commonly used to direct and/or focus light in desirable ways and have remained largely unchanged since their invention nearly 200 years ago. Such surfaces commonly consist of either rigid prism surfaces arranged concentrically on an often flat surface or rigid curved surfaces arranged concentrically often on a flat surface. Fresnel optical devices utilize either diffraction and/or refraction, or reflection to direct light as desired. The general advantages of Fresnel optics include the performance simulation of optical lenses, prisms, and mirrors with a significant reduction of material, thickness and consequently dramatically lighter weight and less bulky optics.
Heretofore, the designs of concentric, flattened lens, prism, and mirror structures have always been rigid and have been otherwise not variable. Commonly these concentric circles were cut or molded into transparent plastic or glass. The angles and curves once cut thereon not being variable. Adding flexibility to similar structures as described herein is now possible due to the many advances in the transparency and elasticity of polymer technology. Transparent highly elastic extrusions welded and assembled as described herein are tunable by increasing and decreasing the quantity of two fluids therein (a first fluid with a first refractive index and a second fluid with a second refractive index). The angles and curves formed by the fluids due to the surfaces there between, due to elastic transparent membrane walls, cause light to be redirected as desired through the processes of refraction and/or diffraction. Moreover identical structures coated with a reflective material and operated identically forms a mirror whereby electromagnetic energy is redirected to a focal point by the process of reflection.
Prior art teaches the use of flexible membranes such as is depicted in FIG. 1 from U.S. Pat. No. 5,684,637 (Floyd, 1997). The membranes are actuated to form a convex lens of desired focal length by varying a fluid with a refractive index contained there between. This structure and those abundantly found in prior art that are similarly actuated when used in small applications can reliably provide a range of focal lengths and coherent focal points. In many applications however, especially where the volume, physical size and weight of fluid are a consideration, an alternate approach utilizing Fresnel structures to provide coherent variable focal lengths is needed. The present invention achieves these objects with significantly reduced thickness, weight and volume.
Prior art teaches the use of a flexible mirror membrane actuated by fluid pressure such as is depicted in FIG. 2 from U.S. Pat. No. 4,890,903 (Treisman et al, 1990). Such a fluid mirror membrane can be used in some small applications where thickness is not a factor. In larger applications or where absolute mirror thickness is a consideration, the variable membrane mirror composed of Fresnel zones as disclosed herein is a usefull unanticipated advancement over the prior art.
Prior art teaches the use of actuating rigid structures to reliably alter the path of electromagnetic energy. FIG. 3 from U.S. Pat. No. 5,166,831 (Hart, 1992) discloses the actuation of rigid planar members to vary a liquid prism angle. This and similar prior art is useful for some small applications. In large applications, the volume, physical size and weight of fluid required in these structures makes them prohibitive engineering problems. To elimnate the engineering problems of prior art, an alternate approach utilizing variable Fresnel structures to variably alter the course of electromagnetic radiation is required. Additionally, the Hart structure can not achieve a variable focal length (nor did Hart intend it to).
Prior art discloses the use of variable lenslets. FIG. 4 from U.S. Pat. No. 5,774,273 (Bornhorst, 1998) depicts a hexagonal grid and a membrane. This system uses fluid pressure to push the membrane through the grid and thereby produces an array of variable lenslets. This lenslet array can not achieve a truly coherent focal point. Nor can this structure reliably deliver a single variable focal point. Additionally, due to the grid structure, much of the electromagnetic radiation is lost into the grid. The hexagonal structure is used to minimize the light loss due to absorption by the grid structure (if the grid had round holes, the grid would absorb even more energy). But the hexagonal structure introduces the problem of lenslet distortion because the curvature of the membrane will be distorted into a rippled curve (caused by non uniform stretching when conforming to the hexagonal shape) when being stretched through anything other than a round structure. The round hole and smooth curve are required for imaging optics. The Bornhorst grid structure forces a compromise between the loss of optical integrity when using a hexagonal grid and loss of optical efficiency when using a round grid. The present invention can achieve the objects of a variable coherent focal point and length with nearly one hundred percent efficiency and with nearly no distortion. For all of these reasons, the new art embodied in the variable Fresnel structure disclosed in the present application is a significant unanticipated advancement over prior art.
Prior art FIG. 5 from U.S. Pat. No. 5,774,273 (Bornhorst, 1998) incorporates several independently variable arrays of fluid pressure variable lenslets into one collective structure. Again, the structure disclosed can not deliver a truly coherent focal point. Nor can it produce a variable focal point. This structure and the actuation methodology is not adequate for the purposes of a coherent variable lens with variable focal point and focal length. Each of these independent lenslet arrays can be directed into a similar direction but their grid shapes and positioning prohibit usage in any imaging optics applications. The new art disclosed in the present application avoids the problems associated with the grid structure by not using one. Further all of the new structures of the present invention can be used together to produce a coherent optic with variable focal length and a true focal point. These are all significant advancements unanticipated, unaddressed, and unachievable by prior art.
The variable prismatic surface of prior art FIG. 6 from U.S. Pat. No. 5,774,273 (Bornhorst, 1998) can incoherently simulate a focal point. This may be adequate for some imprecise lighting applications but is not adequate for any coherent applications. Specifically since the riser of the structure is not parallel to the light source, (but instead forms a second surface in the path of the light) a high percentage of light is either absorbed, reflected, or refracted by the secondary angle formed by the riser. This causes light rays to travel in undesired directions and further increases waste within the system Waste of energy may be tolerable where excess energy can be pumped into the system such as in some lighting applications where efficiency is not a factor. But such waste is not tolerable in a coherent optical system especially where input energy is finite. Moreover the art taught in Bornhorst teaches that lenslet surfaces may be either variable with respect to curvature or be variable with respect to angle. None of the prior art membranes are variable with respect to both angular pitch and curvature. The new art disclosed in the present application efficiently and coherently redirects electromagnetic energy. Surfaces of the present application are true variable concentric Fresnel structures that can be varied with respect to angular pitch and curvature simultaneously.
After a review of prior art it becomes clear that a coherent variable focal length lens with a true focal point in the form of a concentric Fresnel structure has neither been anticipated nor achieved in the prior art. Thus, the new art disclosed herein solves problems unanticipated and unaddressed in the prior art. Disclosed herein is the use of concentric elastic stretchable and collapsible surfaces which enable one optical device to incorporate alterable Fresnel zones or surface angles and surface curves. Such alterations are made to be permanently variable such that one optical device has alterable focal lengths or can otherwise continually be reconfigured in real time to redirect electromagnetic radiation as desired.
Our society increasing relies on accurately and reliably directing electromagnetic radiation for communications, science, photography, illumination, entertainment, telescopy, medicine, and magnification etc. Flexible concentric circular structures as described herein add important advantages for these and other important objects. Moreover, abundant and valuable benefits provided by such structures have been heretofore unrecognized and not addressed in prior art.
In the lens embodiment, the invention described herein incorporates a first fluid with a first refractive index in a first series of concentric zones and a second fluid with a second refractive index in a coplanar second series of concentric zones. The two zones being adjacent to one another alternating between a concentric circle of the first then a concentric circle of the second then the first and etc. Wherein each circular zone in the series of first and second fluid zones are separated by a transparent barrier with elasticity. Additionally, fluid can be added or subtracted to each concentric circle as desired through ports in their otherwise sealed chambers. The structure and process described produces a refractive and/or diffractive optical component which is variable as to its focal length and transmittance direction. In the lens embodiment, a reflective material is covering the membrane to produce a Fresnel mirror with a focal point.
Accordingly, several objects and advantages of my invention are apparent. Lenses and mirrors manufactured by the method described have alterable focal lengths. Once deployed in the field they can be tuned to direct electromagnetic energy as desired. They then can be retuned to many different specifications repeatedly and predictably. The applications for lenses and mirrors with a variable focus length are far too numerous to individually enumerate herein. Clearly objects such as illumination, entertainment, communications, science, photography, telescopy, medicine, and magnification (among many others) will all benefit from this new technology.
Further objects and advantages will become apparent from a consideration of the drawings and ensuing description.